1. Field of the Invention
The present invention relates to a light-emitting device. More specifically, the present invention relates to a light-emitting device formed from a nitride semiconductor. In the present invention, a “light-emitting device” may refer solely to a semiconductor element or a semiconductor chip formed essentially from a nitride semiconductor substrate and a semiconductor layer laminated thereon, or may refer solely to a device wherein a semiconductor chip is mounted on a mounting part and sealed in resin. Also, the term may be used with both of these meanings at the same time. The semiconductor chip may also be referred to simply as a “chip”. Also, in a chip, the substrate and the epitaxial layer formed thereon may be referred to simply as a “substrate”.
2. Description of the Background Art
Currently, white light-emitting diodes (LED) are frequently used for illumination and compact electronic devices such as portable information terminals. However, there is the potential that they may be used for illumination in large spaces or over large areas in the future. To make it possible to use LEDs for illumination of large spaces and large areas, the light output of LEDs must be increased.
One strategy for increasing LED light output is to allow the light generated within the LED to be efficiently output to the outside, i.e., to improve light extraction efficiency. In one proposed technology for improving light extraction efficiency, e.g., see Japanese Laid-Open Patent Publication Number 2003-69075, a nitride semiconductor layer is grown on a base substrate formed from sapphire or the like. The base substrate is removed from the grown nitride semiconductor layer, and the surface of the resulting nitride semiconductor substrate formed from this nitride semiconductor layer is processed by wet etching, dry etching, abrasion, or the like to form cavities and projections (i.e., to form a non-specular surface). In Japanese Laid-Open Patent Publication Number 2003-69075, the formation of these cavities and projections reduces optical interference caused by multiple reflections in the nitride semiconductor substrate, thus improving light extraction efficiency.
However, in the technology described in Japanese Laid-Open Patent Publication Number 2003-69075, if wet etching, which is the simplest method for forming cavities and projections, is used, and electrodes have already been formed on the nitride semiconductor substrate surface, the wet etching operation may damage the electrodes (or may remove the electrodes). This prevents the predetermined current from being supplied from the electrodes to the light-emitting device, resulting in the inability to perform as a light-emitting device and the inability to provide a light-emitting device with improved light extraction efficiency.
The object of the present invention is to overcome the problems described above and to provide a light-emitting device with improved light extraction efficiency.